The Health Report: New HIV vaccine

For this study, however, researchers used a so-called 'mosaic' vaccine that combines pieces of different HIV virus types in order to elicit an immune response against various HIV strains.

In 2015, Professor Barouch and his colleagues tested various combinations of the mosaic vaccine in healthy adults in east Africa, South Africa, Thailand and the US.

The 393 participants were given four vaccinations over the course of 48 weeks. Each vaccine combination was found to be safe and "well tolerated" and produced an anti-HIV immune response.

At the same time, researchers administered the 'mosaic' vaccine combinations to 72 monkeys to test for resistance against a HIV-like virus that affects monkeys — the simian-human immunodeficiency virus.

They found the vaccine that produced the greatest immune response in humans also provided the best protection in monkeys.

"Because of the protection in monkeys, and the safety and immune responses in humans, the vaccine has been advanced into a larger scale study … which will determine whether it can prevent HIV infections in humans."

Fifth vaccine trial to make it this far

Since the emergence of the HIV epidemic in the early 1980s, just four experimental vaccines have ever been evaluated for efficacy in humans, and only one has shown evidence of protecting against HIV.

A vaccine tested among 16,000 Thai volunteers in 2009 lowered the rate of human infection by 31 per cent, but that effect was considered too low for the drug to be pursued for widespread use.

Professor Barouch said although the 'mosaic' vaccine had triggered a promising anti-HIV response in humans, there was no guarantee it would be enough to prevent HIV infection.

"The challenges in the development of an HIV vaccine are unprecedented, and the ability to induce HIV specific immune responses does not necessarily indicate that a vaccine will protect humans from HIV infection," he said.

Leading infectious diseases expert Sharon Lewin from the Doherty Institute said the research was "interesting" but that there was still a way to go before an effective HIV vaccine was available.

"There's been a very chequered history here of vaccines looking good in monkeys and then you move them into humans and they don't work," said Professor Lewin.

"That has happened before… but they are using a slightly more sophisticated method in this instance."

Vaccine critical to eradicate HIV

Despite significant advances in our understanding of HIV and its prevention and treatment, the development of a preventative vaccine remains urgent.

The vast majority of people living with HIV are in low- and middle-income countries, particularly in Sub-Saharan Africa, where they (and the people at risk of HIV) often do not have access to prevention, care, or treatment, and there is still no cure.

"What several countries around the world have shown, including in Australia, but New South Wales in particular, is that if you get treatment and PrEP use up to high levels, you start to see a reduction in new HIV infection," Professor Lewin said.

PrEP, however, must be taken daily, is not a sustainable long-term strategy for tackling HIV on a global scale, she said.

"PrEP is very effective, and while we don't have a vaccine, we definitely need to roll it out … we still have 1,000 new HIV infections a year in Australia," she said.

"But it costs money, you need to be in regular healthcare, and it requires a whole infrastructure to support it … which is why any infectious disease that's ever been effectively tackled has always been associated with a vaccine."

Australia has 'impressive track record' of HIV treatment

In 2016, it was estimated more than 26,000 Australians were living with HIV, according to the Kirby Institute at the University of New South Wales.

"Australia has an extremely impressive track record of HIV testing, uptake of treatment, and staying on treatment," Professor Lewin said.

That's thanks in large part to the introduction of lifelong virus-suppressing antiretroviral therapy in 1995, which revolutionised the treatment of HIV worldwide.

"So, if you treat people [with antiretroviral drugs], the amount of their virus shrinks down to very low levels. It's always there, but at very low levels, so you block transmission," Professor Lewin said.

The treatment reduces the risk of disease advancement associated with HIV, meaning people on daily treatment can live a long and healthy life.

The International AIDS Conference will be held in Amsterdam from July 23 to 27.

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